Apparatus for heating oils



Feb. 1;, 1947. BOGK 2,415,726

APPARATUS FOR HEATING OILS Filed Dec. 2, 1943 O00OO0OOO000000000000000007000000000 o O O O OOOOOOOQiOOOOOOOOOOO N N 07 h N O000000000OOOOOOOOOOOOOOOOOO 00000000000 OOOOODOOOOOOOOOOOO 0005 I] 23 I9 I I INVENTOR J. E. BOGK I ATTo Patented Feb. 11, 1947 UNITED STATES PATENT OFFICE Phillips Petroleum Com Delaware pany, a corporation of Application December 2, 1943, Serial No. 512,643

2 Claims.

This invention relates 'to apparatus for heating of fluids. More particularly, this invention relates to an improved furnace suitable for heating petroleum hydrocarbons to temperatures required for pyrolysis.

Uniform and controlled heating of oil by means of furnaces has long been a problem in the petroleum industry. The introduction of the pipe still or furnace in which oil is passed through tubes heated by radiation, convection, or a combination of the two was a great step forward in the art of cracking petroleum oils. The pipe still in itself, however, did not immediately solve the problems and difficulties attendant upon the use of the older type shell stills. While heating by convection is successfully carried out in banks of tubes, and heating by radiation may be rather uniformly distributed over the surface presented by a series of tubes, troublesome localized overheating in spots is still encountered. Localized overheating results in hot spots which form coke on the inside of the tube. This coking prevents rapid transfer of heat from the wall of the tube to the oil inside thereby aggravating the condition, often to the extent that the tube fails and must be replaced. The operation of a furnace for heating hydrocarbon oils must be flexible to compensate for changes in the compositions of the feed material, and of the fuels available for firing. Various furnaces have been devised and various methods of furnace operation proposed to eliminate some of the problems encountered in pyrolysis of hydrocarbons.

The present invention provides apparatus and methods of operation of this apparatus designed to eliminate or substantially reduce the inherent troublesome aspects of pyrolysis of hydrocarbon oils in tube stills. The combination of features provided in this invention results in system possessing great flexibility in operation.

An object of this invention is to provide improved apparatus for heating hydrocarbon oils.

Another object of this invention is to provide an improved method of operating furnaces for pyrolysis of oils.

Another object-of this invention is to .pI'OVidB means for increasing the heat transfer in the convection section of such a furnace.

Another object of this invention is to provide means effecting rapid heating and even distribution of heat in the radiant section of such a furnace. v

Other objects and advantages will be apparent from the following detailed description and -the accompanying drawing showing a specific embodiment of apparatus of this invention in vertical cross section.

With reference to the drawing, the main or' radiant section of the furnace comprises a supporting framework comprising a structural steel framework made up of vertical supports is mounted on a base ll. The vertical supports H3 are tied together at the top by the cross pieces 12 making a rigid framework for the furnace. The structure defined by the framework is covered by a suitable roof '13 for protection against Weather. The walls, roof, and floor of the radiant section are shown as made up of panel sections i l, 55, and I6, respectively. These panel sections are made up of refractory material supported on a suitable backing or foundation with provision for attaching the panels to the supporting framework of the furnace. The panel construction preferred for use is described in detail in U. S. Patent No. 2,315,833, of April 6, 1943. The wall panels I l are attached to and supported by the vertical steel supporting members l0. Roof panels l5 are attached to and supported by I beams 18 carried by the members H1. Floor panels 16 are supported on sand, alumina, or other heat resistant matrix. The end wall 20 is of the same panel construction as the side walls. The interior of the walls are coated with a refractory material which, when dry, is exceptionally light in color. Suitable materials of this type are those known by the trade names Panalag, Insulclad, and .Insulag Which are of secret composition and made by Quigley Company, Inc -New York, N. Y. This coating increases the heat to the tubes by wall radiation and minimizes the loss of heat through the furnace-wa-lls.

The wall tubes in the radiant sectionof the furnace are indicated by the numeral 22, floor tubes, by numeral 23, and roof tubes, by numeral 24. The tubes are disposed along the floor, 'ceiling, and the side walls, with the exception of the wall space required for the burners. The tube arrangement gives a close approach to complete coverage of these surfaces, approaching the socalled black surface or cold surface. The end walls '23 are not provided with tubes when firing from the side as illustrated in the drawing. Reradiatio-n from the end walls is evenly distributed over the tubes alon the side Walls, floor, and ceiling. This coverage makes possible very even heat transfer rates throughout the radiantsection of "the furnace substantially unaffec't'ed by reradiation of exposed refractory surfaces opposite 'anyof the banks of tubes. The

tubes are arranged in single rows at a spacing from the refractory surface which has been found to give a more even distribution of heat circumferentially of the tubes than is possible by means of the conventional arrangement in which the tubes are placed relatively closer to the furnace wall. The tubes are spaced, center to center, at adistance equal to about 2.4.- times the outside diameter of the tubes. Thus 3 /2 inch 0. D. tubes are set on centers about 8 inches apart. For the top tubes, the distance from the tube center to the refractory surface is equal to the center to center spacing of the tubes. For the side wall tubes distance from the refractory to the tube center is 1.1 times the center to center spacing, while for the floor tubes this distance is double the center to center spacing. Thus for 3 /2 inch 0. D. tubes, the distance from the refractory to the tube centers is about 8 inches for the top tubes, 8.8 inches for the wall tubes and 16 inches for the fiocr tubes. This spacing avoids the tendency to local overheating of the inside face of the tubes.

The burners are of any suitable type; various types for use with gas, liquid, and solid fuels are available. The burners 25 are placed, in the modification illustrated, along the side wall. Secondary air may be admitted through ports 25 and 21 placed adjacent the burners. Flow of secondary air through these ports is controlled by the dampers 28 and 29. Forced draft to the burners and secondary air inlets is provided by a hood 30 to which air is supplied by a blower M. The absorption of heat by the floor tubes can be controlled to some extent by adjusting the dampers 29 to regulate the flow of secondary air through the ports 2'? below the burners. The floor tubes can be blanketed, if desired, by control of secondary air in this manner. Alternative arrangements of the burners may be resorted to without departing from the advantages resulting from the novel construction of the radiant section of the furnace of this invention. For example, the burners may be installed in the end walls or in the fioor of the furnace with rearrangement of tubes to provide coverage of the space not occupied by the burners. When the furnace is fired from the fioor, as is known in the art, it will be evident that the floor tubes will be removed to provide free space for the burners and that these tubes may then be advantageously placed at the ends of the furnace.

From the main or radiant section of the furnace, the products of combustion pass to a segregated auxiliary or convection section supported by the vertical supporting members All tied together by the beams 4|, 42, and 43. The framework thus made up is tied to the framework of the radiant section by the beams 44 and 45. The beams s4 and 45 also serve to support the refractory sections 45 defining the duct 41 for transfer of combustion gases from the radiant section of the furnace to the convection section. The convection section is made up of sections 48 of insulating panels similar to those used in the radiant section of the furnace. A stack 49 controlled by the damper 50 is provided to conduct combustion products from the convection section. The tubes are placed in a bank which serves to extract heat from the gaseous products of combustion leaving the radiant section of the furnace. The lowermost rows of the bank of tubes 5! are subject to some radiant heat from the radiant section through the duct 41 and to reradiation from panels 46. The gaseous products of com- 4. bustion are recirculated in the convection section by means of a blower 52 which takes gases from the upper part of the convection section through pipe 53 and passes these gases through pipe 54 to the lower part of this section. The flow of recirculated gases is controlled by dampers 55 and 56. Burners 58 in the convection section may be used as desired to supply additional heat to the furnace at this point.

The segregation of the convection section from the radiant section of the furnace is an important feature of this invention which provides many advantages. This construction gives the entire main furnace housing to combustion space and radiant surface. This space is the largest available space. for a given size housing. The space conventionally used for convection tubes and bridge wall has been eliminated. For a given size firebox (combustion space) the construction used requires a minimum span on the roof arch and minimum strength of supporting material, thereby resulting in economy of construction. The firebox is of such size as not to be restricted to firing with any specific burner or any particular fuel. Gas, oil, or solid fuel may be used for firing, either exclusively or in combination. The segregated convection section allows recirculation of the products of combustion over the tubes in this section, without interference with the firing of the main or radiant section of the furnace. The convection section may be fired separately by use of the burners provided therefor without interference with the firing of the radiant section of the furnace. These and other advantages not heretofore realized are obtained by the novel construction of the furnace of this invention. It will be evident that this invention provides for great flexibility in operation and that the furnace herein described may be used with a variety of feed stocks with optimum heat transfer conditions for each.

The feed may be introduced to tubes 51 in the convection section of the furnace for preheating as illustrated and then passed to the radiant section Where it is subjected to conditions effecting pyrolysis, In the tubes along the walls and floor the fluid is heated rapidly to the reaction temperature without excessive overheating in localized areas. The tubes along the top of the radiant section allow for the desired residenc time at reaction temperature after which the effluent may be withdrawn from the radiant section at the point illustrated. It will be evident to one skilled in the art that flow is not restricted to the path illustrated and described and that the flow may be otherwise directed as desired.

The path of gases leaving the radiant section of the furnace is such that only one right angle turn is required between the firebox proper and the fiue gas exit to the stack. This results in economy in construction in providing either forced or natural draft required for operation. The furnace is very sensitive to draft changes. By control of dampers and balancing primary and secondary air at the various intakes the heat pickup in the convection section and in various parts of the radiant section can be adjusted to best suit the requirements of the stock being processed. v

'The large percentage of radiant surface permits a required amount of heat to be transmitted to the tubes under mild heat transfer rates. In selecting tubing materials on a creep-strength basis, economy of materials and long tube life are realized due to the lower heat transfer rate factor obtainable in a furnace'of given size constructed in accordance with this invention. Due to the large percentage of radiant heat absorption and the maximum coverage of furnace walls with tubes, the firebox and stack temperature are appreciably lower than in conventional furnaces, thereby giving increased maintenance life on the furnace refractory lining. This protection also extends to the back wall in the convection section below the main bank of convection tubes.

The large radiant surface allows a very quick heat to high temperature on the oil procesed. As will be apparent to those skilled in the art this quick heating minimizes effect of requiring addition of heat of reaction to sensible heat requirements when an external reaction zone is used in conjunction with the furnace. It also minimizes side effects of additional heat of reaction, such as coke formation within the furnace proper, in such processes. The quick heating being secured in such a short time originally, the effect of change of time of process stock in tubes with changes in pressure caused by some change in related external operation is minimized.

The main stack damper 59 is arranged so that each end of the damper shaft 58 is supported by a bearing 59 at a point outside and independent of the stack breeching so that damper operation is not affected by temperature variations in the stack proper. The relative location of the stack damper control means 69 to the burners makes a convenient location for manual control of the damper from the firing aisle of the furnace.

I claim:

1. A furnace for heating oil which comprises a main section having refractory side walls, end walls, floor, and roof; burners along the lower portion of one of said side walls of the main section for combustion of fuel therein; means for introducing secondary air to the main section at points adjacent said burners; a row of horizontally spaced horizontal tubes adjacent the floor; a row of vertically spaced horizontal tubes adjacent the side wall opposite the burners; a row of horizontally spaced horizontal tubes adjacent the roof; an outlet for heated gases in the side wall at a point above the burners and below the level of the roof; a row of vertically spaced horizontal tubes adjacent the side wall between the burner and the outlet; a row of vertically spaced horizontal tubes adjacent the side wall between the outlet and the roof; an auxiliary section segregated from the main section and elevated relative to said main section to a point above the burners of said main section; vertical refractory walls enclosing the auxiliary section; an inlet in the lower part of one wall of the auxiliary section opposite the outlet from the main section; an outlet for heated gases at the top of the auxiliary section; a duct communicating the outlet of the main section with the inlet of the auxiliary section providing a passage for transfer of heated gases and for transmitting radiant heat from the main section to the auxiliary section; a row of vertically spaced horizontal tubes adjacent the wall opposite the inlet in the auxiliary section and receiving radiant heat transmitted by said duct; a plurality of rows of horizontally and vertically spaced tubes between the inlet and the outlet of the auxiliary section in the path of flow of heated gases from said inlet to said outlet; means for Withdrawing gases from a point in the auxiliary section adjacent the outlet thereof and returning said gases to said auxiliary section at a point adjacent the inlet thereof; and burners adjacent the inlet of the auxiliary section for generating heat in said auxiliary section by combustion of fuel therein.

2. In the combination of claim 1, the tubes in each row on said side walls, floor and roof being spaced on centers about 2.4 times the outside diameter of the tubes, the floor tubes being spaced from the floor a distance twice the center spacing of the tubes, the top tubes being spaced from the roof a distance substantially equal to the center spacing of the tubes, and the side wall tubes being spaced from the side walls a distance of about 1.1 times the center spacing of the tubes.

JOHN E. BOGK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,869,626 Spencer Aug. 2, 1932 2,035,037 Youker Mar. 24, 1936 2,108,688 Mekler Feb. 15, 1938 2,129,589 Praeger Sept. 6, 1938 2,146,497 Barnes Feb. 7, 1939 2,147,609 Reed Feb; 14, 1939 2,165,725 Pelzer July 11, 1939 2,326,473 Lyster Aug. 10, 1943 2,335,317 Sherman Nov. 30, 1943 1,901,970 Huff Mar. 21, 1933 2,076,854 Mekler Apr. 13, 1937 2,224,917 Mekler Dec. 17, 1940 2,249,697 Rickerman July 15, 1941 2,311,421 Ward Feb. 16, 1943 2,363,266 Schauble Nov. 21, 1944 OTHER REFERENCES Mekler, I-Ieaters; The Science of Petroleum; vol. 3 (1938); pages 22232232 (pages 2224 and 2225 pertinent). (Copy in Division 31.) 

